1. Field
The disclosed embodiments relate to a system for opening and closing a landing-gear compartment of an aircraft.
The disclosed embodiments find application in aeronautics and especially in the field of hatches for closing aircraft landing-gear compartments.
2. Description of the Prior Art
A landing-gear compartment is a housing designed to receive a landing gear of an aircraft. In most aircraft used to carry goods or people, the gear compartment is situated in the fuselage of the aircraft. The gear compartment is generally closed by an opening and closing system comprising several hatches. These hatches can be of several kinds. Conventionally, an opening and closing system or hatch system comprises at least two main hatches, for example front gear hatches which open to enable the landing gear to be lowered and which close when the gear is extended. It can also comprise at least two secondary hatches, for example rear gear hatches which open to enable the lowering of the gear and remain open so long as the gear is extended. It may also comprise a first hatch, called a central hatch or main leg fairing which, like the secondary hatches, remains open so long as the gear is extended.
A landing-gear hatch, more simply called a gear hatch, usually has a panel fixed to hinge arms. Generally, these hinge arms are goose-necked features hinged on the structure of the aircraft, about a pivoting shaft offset towards the interior of the landing gear relative to the panel. The goose-necked features are generally distributed along the length of the hatch and are fixed on the one hand to the hatch and on the other hand to the structure of the aircraft. At least one goose-necked feature is connected, by means of a link-rod, to the structure of the aircraft. This link-rod enables a motion of rotation of the hatch relative to the fairing of the aircraft. Thus, when the landing gear is extended, the pivoting of the hatch out of the fuselage is obtained by means of the link-rod and the goose-necked hinges.
At present, each secondary hatch is connected to the landing gear by a direct link. This direct link consists of a link-rod fixed on the one hand to the landing gear, for example on the gear leg and, on the other hand, to the hatch. This link-rod enables the hatch to be maneuvered directly according to the motions of the landing gear. Thus, when the landing gear is retracted, the very fact that the landing gear rises into the landing-gear compartment causes the hatch to close. At the same time, when the landing gear is extended, this direct link enables the hatch to be opened by pushing said hatch out of the fuselage. More specifically, when the gear is extended, it rotates about an axis giving rise to a translation motion of the link-rod which pushes the hatch to its open position. A direct link of this kind therefore enables the extension of the landing gear and the opening of the hatch to be controlled at the same time.
To preserve the aerodynamic qualities of the aircraft fuselage, the arrangement of the pivoting shaft of the landing gear is done within the gear compartment. The hatches close after having let through the landing gear in order to minimize aerodynamic disturbance. For aerodynamic reasons, the secondary hatches have a minimum surface area and aperture enabling the deployment of the landing gear. Indeed, since the secondary hatches remain open so long as the gear is out, it is important to achieve the maximum reduction in the number and surface area of the elements likely to create disturbance in the flow of fluids along the fuselage of the aircraft.
At present, in most aircraft, the gear compartment is closed by means of an opening and closing system comprising four or five hatches. In the case of a four-hatch system, there are generally two rear hatches or secondary hatches and two front hatches or main hatches placed side by side.
In the case of a five-hatch system, there are generally two front hatches, two rear hatches and one central hatch or main leg fairing. An example of a five-hatch system is shown in FIG. 1. The two front hatches 1 and 2, namely the main hatches are large-sized hatches enabling the passage of the entire landing gear. These front hatches open on either side of the fuselage of the aircraft, perpendicular to the fuselage, so that only the thickness of the hatches forms an obstacle to the path of flow of the fluids. In other words, the front hatches open transversally, respectively to the right and to the left of the fuselage of the aircraft.
In this five-hatch system, the two rear hatches 3 and 4, or secondary hatches, open like the front hatches, on either side of the fuselage of the aircraft, perpendicularly to the fuselage. The rear hatches therefore also have a transversal opening, respectively to the right and to the left of the aircraft fuselage. As shown in FIG. 2, when the rear hatches 3 and 4 are open, they are situated on either side of the leg of the landing gear 6, substantially in the same plane as the tires 7 of the landing gear. As explained here above, the rear hatches 3 and 4 are each actuated by means of a link-rod fixed on the one hand to the gear and, on the other hand, to the hatch. Thus, the extension of the landing gear has the effect of pushing the rear hatches out of the fuselage of the aircraft.
In this five-hatch system, the main leg fairing 5 is connected rigidly to the landing gear. As is shown in FIG. 3, the main leg fairing 5 is linked solely to the landing gear. It has no hinge with the fairing. Indeed, as can be seen in FIGS. 1 and 3, the main leg fairing 5 is situated between the front hatches, along the rear hatches. It is connected neither to the fuselage of the aircraft nor to the other hatches. It is connected only to the landing gear. Thus, when the landing gear gets extended, the main leg fairing 5 is lowered along the gear leg 6, as can be seen in FIG. 2, and remains along the gear leg so long as the landing gear is extended.
In certain aircraft, especially cargo aircraft designed solely for freight operations, there may exist certain constraints as regards the positioning of the floor. For, in certain cases, goods transporters need to be able to load their goods by means of wheeled trolleys inside the aircraft. To this end, the aircraft floor needs to be plane, i.e. it must form a zero or near-zero angle with the horizontal. Now, certain aircraft have a non-plane floor forming an angle of 1 to 2 degrees with the horizontal. To reduce this angle without however modifying the entire aircraft, the floor can be lifted so that it has a near-zero angle relative to the horizontal. A simpler technique to raise the floor consists in raising the nose of the aircraft when it is on the ground, for example by increasing the height of the landing gear.
To modify this height of the landing gear, it is possible to modify the design of the gear itself. Now, this would entail considerable cost, both for the designing of the gear and for the replacement of the landing gear on the aircraft, depending on the goods or passengers to be carried.
To modify the height of the landing gear without modifying the design of the gear, it is possible to modify the point of rotation of the landing gear so that it is situated at a lower position within the aircraft. This has the effect of raising the nose of the aircraft, thus straightening the slope of the floor. To this end, it is chosen to lower the axis of rotation of the landing gear. Now, this technique has the direct consequence of shifting the axis of rotation of the landing gear out of the fuselage, i.e. beneath the classic fairing of the aircraft. The fairing of the aircraft then needs to be modified so as to make it incorporate the offset part of the gear. The new fairing is then domed. It forms a sort of protuberance relative to the fuselage of the aircraft. FIG. 4 is a schematic sectional view of an aircraft fuselage 8 equipped with a fairing of this kind. In this figure, the reference 81 represents an example of a fuselage. In the case of a classic fuselage, the hatch system would be situated at the position of the dashes 83. In the case of an aircraft whose gear height has been modified, the fuselage has a fairing that forms a protruding feature 82. This protruding feather 82 has direct consequences for the system of opening and closing the landing-gear compartment. Indeed, this gives rise to an increase in the surface area of the hatches which has the direct effect of increasing the mass of the hatches and hence the total mass of the aircraft and of modifying the clearances between the goose-necked features that connect the hatches and the fairing. This modification of the clearances between the goose-necked features causes problems relating to the play of the hatches, at the corners of the rotating link-rods used to open the rear hatches.
Furthermore, the pre-stress needed on the front hatches is kept. This pre-stress serves to optimize the flow along the aircraft and prevent the hatches from vibrating because of a pressure difference.
Besides, with a five-hatch system adapted to the modified fairing, the transmission forces on the rear hatches are excessive. This may give rise to vibrations in the hatches. To resolve this problem of transmission of forces, it would be necessary to oversize the link-rods, and the effect of this would be to make it difficult to open the hatches using these oversized link-rods. Furthermore, these oversized link-rods would have to provide for a clearance for the hatches at a maximum angle of 170° of the rotating link-rods and, at the least vibration, would risk exceeding their angular limit of 180°. After this angle has been crossed, there is a risk that these hatches would go in the wrong direction from the kinematic point of view and therefore cause deterioration in the system.